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TCP over Bluetooth: Simulation and Performance

This study explores the performance of TCP over Bluetooth, focusing on its efficiency and fairness in piconet networks compared to traditional 802.11 networks. It investigates the impact of connection delays and gateway hops on throughput and fairness, utilizing simulation tools like Glomosim. Key aspects include Bluetooth's unique polling schemes and the behavior of connections across interconnected piconets. Future work aims to refine packet sizes, buffer effects, and compare different TCP implementations, enhancing our understanding of Bluetooth's capabilities in wireless communication.

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TCP over Bluetooth: Simulation and Performance

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  1. TCP over Bluetooth: Simulation and Performance Members: Raymond Liu raymondl@ucla.edu Tutor: Yeng-Zhong Lee yenglee@cs.ucla.edu

  2. Outline • Introduction • Motivation • Goal • Simulation Design

  3. Introduction • Bluetooth vs 802.11 • Similarities • Radio frequency at ≈ 2.4 - 2.5 GHz • Differences • Power consumption, communication range, price • Frequency hopping spread spectrum = FH-CDMA  DSSS (Direct sequence spread spectrum) = DS-CDMA • Nodes must be organized in Piconets

  4. Bluetooth vs 802.11

  5. Introduction (Cont.) • Bluetooth • No hidden terminal • Piconet • One master, up to 7 slaves, uses frequency hopping code to reduce interference • Master controls access by polling slaves • No slave-slave or master-master communication • Scatternet • Group of piconets connected by gateways • Gateways connect piconets in a scatternet • Gateways use TDD to switch between piconets • TDD (Time Division Duplexing) of gateways left open

  6. Bluetooth Scatternet

  7. Introduction (Cont.) • 802.11, TCP has sometimes been shown to degrade fairness • For 802.11, it has been shown that TCP with window size > 1 only increases collisions, thus degrading throughput • Bluetooth alleviates those problems of collision with separate domains/piconets

  8. Polling Schemes and Gateways • Static-cyclic polling scheme • Slaves are polled in a fixed order in all polling cycles • Flows may consistently capture the bandwidth of others’ due to limited queue for each slave • Flows across the scatternet will contend for the queues of gateways • Fairness issues? • Pseudo-cyclic polling scheme • Slaves are polled in a dynamically decided random order • Piconets coordinate and share gateways according to an agreed superframe cycle; does not allow for pseudo-cyclic polling; must use gateway at allocated time

  9. Our Study • How does TCP behave over Bluetooth? • Focus on Fairness/Capture behavior • Effect of large delays • connections across scatternet through multiple gateways; how good can throughput and fairness be? • large delay vs. short delay; does short delay capture? • Is there a maximum number of gateway hops that a flow can go through while still maintaining a “good” performance of TCP?

  10. Simulation • Glomosim • Bluetooth implementation given to us by tutor • Frequency hopping pattern mechanism allows the overlapping of different piconets in the same space without a significant increase of interference • Structure and TDD are predetermined in configuration files • Use FTP model of connections in Glomosim

  11. Simulation • Assumptions • Masters are full time in piconet and do not become slaves in other piconets • Up to 2 gateways between piconets • Stick to simple topologies of scatternets: linear/chain, ring, and possibly grid • Gateways become bottleneck, routing predictable • Node placement random, in unpartitioned space, with no mobility of nodes

  12. Simulation Throughput between adjacent piconets i and j with one gateway b(i,j) = min( b * fi, b * fi) si + overhead(si) sj + overhead(sj) b = Bluetooth throughput sx = # nodes active when gateway present fx = proportion of time gateway in piconet We prevent FTP connections from having the same sources or destinations, so si = sj, and we set TDM of gateways to ½ & ½ to maximize throughput

  13. Simulation • Different scenarios • Connections with same number of gateway hops vs. longer and shorter connections • Flows going in same direction vs. bidirectional traffic across scatternet • Effect of master vs. slave as source or destination • Lines/chains, rings, grids

  14. Status of Experiment • Analyzing current results • Investigating variations in results caused by simulation environment • Considering more data sets to simulate, variations to try

  15. Future/Ongoing Work: • Smaller packet size • Decrease effects caused by delay? • Buffer size • Smaller buffers’ effect on capture • TCP Congestion window size • How bandwidth is affected by # of gateways • Effectiveness of RED polling schemes • Compare different TCP implementations (Tahoe, Reno, Westwood, …)

  16. Thanks!

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